JP2015129646A - Radar device and method for measuring distance and speed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radar device for measuring the distance and speed of an object with high accuracy at low cost.SOLUTION: A laser beam outputted from a laser 10 is intensity-modulated with a periodic signal from an oscillator 11 by a modulator 12 before being outputted. The periodic signal is a cosine wave, the frequency of which is a minimum value f0 at which a Doppler frequency fd can be measured. The laser beam reflected by an object is subjected to optical heterodyne detection by a multiplexer 16 and a photodetector 17 before being inputted to a BPF 18 and 19, respectively. The electric signal inputted to the BPF 18 is passed for only a band near the frequency f0 and the passed signal is inputted to phase difference detection means 20. A distance is calculated by comparing a difference in phase between the periodic signal from the oscillator 11 and the periodic signal. On the other hand, the electric signal inputted to the BPF 19 is passed for only a band near the fd, and the passed signal is inputted to frequency analysis means 21. Then, a frequency spectrum is calculated, and a speed is calculated from the Doppler frequency fd.

Description

  The present invention relates to a radar apparatus that irradiates an object with laser light, detects the laser light reflected by the object, and measures the distance and speed of the object. The present invention also relates to a distance speed measurement method.

  2. Description of the Related Art A radar apparatus (LIDAR) that measures the distance and speed of an object by irradiating the object with laser light and receiving and analyzing the laser light reflected by the object is conventionally known. The FMCW method is known as a distance and speed measurement method (for example, Patent Document 1). In the FMCW system, laser light is frequency-modulated and irradiated, the received laser light and local light are optically heterodyne detected to generate a beat signal, and the distance and speed are obtained by frequency analysis.

JP 2001-324563 A

  However, in the measurement of distance speed by the FMCW method using laser light, a high-speed AD converter is necessary to increase the resolution, and there are technical and cost problems.

  Accordingly, an object of the present invention is to realize a radar apparatus that can measure distance and speed at low cost and with high accuracy.

  The present invention relates to a radar apparatus that measures the distance to an object and the speed of the object by irradiating the object with laser light and detecting and analyzing the laser light reflected by the object. Transmitting means for irradiating the object with laser light intensity-modulated with a periodic signal having a frequency f0 smaller than the minimum value of the Doppler frequency fd measurable by movement; and receiving means for receiving the laser light reflected by the object; The detection means for combining the laser light received by the reception means and the laser light before transmission for optical heterodyne detection and converting them into an electrical signal, and the frequency f0 component of the electrical signal from the detection means and the periodic signal A phase difference detecting means for detecting a phase difference and measuring a distance to the object, and an electric signal from the detecting means are subjected to frequency analysis to obtain a Doppler frequency fd. A frequency analysis means for measuring a radar apparatus characterized by having a.

  It is desirable to provide a first filter having the following pass characteristics between the detection means and the phase difference detection means. The first filter is a filter that outputs a frequency band not higher than f1 and passing through a frequency band equal to or lower than f1, with a predetermined frequency not lower than f0 and not higher than Doppler frequency fd being transmitted. By providing such a first filter, signal processing in the phase difference detection means 20 can be facilitated, and distance measurement accuracy can be improved.

  It is desirable to provide a second filter having the following pass characteristics between the detection means and the frequency analysis means. The second filter passes through a frequency band of f2 or higher, where f1 is a predetermined frequency that is higher than frequency f0 and lower than or equal to Doppler frequency fd, and f2 is predetermined frequency that is higher than or equal to f1 and lower than or equal to Doppler frequency fd. This is a filter that cuts off other bands and outputs the result. By providing such a second filter, signal processing in the frequency analysis means 21 can be facilitated and speed measurement accuracy can be improved.

  As the periodic signal, an arbitrary periodic signal such as a cosine wave, a rectangular wave, a triangular wave, or a sawtooth wave can be used. In particular, it is desirable to use a cosine wave. Measurement sensitivity and measurement accuracy can be improved.

  Of the configuration of the radar apparatus, a portion that processes laser light, that is, a transmission unit, a reception unit, and a detection unit may be configured by an optical integrated circuit. The radar apparatus of the present invention can be realized at a lower cost.

  For example, the following method can be used for measuring the direction of speed.

  One is a first detecting means for detecting optical heterodyne by combining the laser light received by the receiving means and the laser light before transmission as the detecting means, and the laser light received by the receiving means and the laser light before transmission. Among them, one having a second detection means that shifts one phase by 90 ° and multiplexes and optical heterodyne detection is used. Then, the frequency analysis means calculates a Doppler frequency fd by performing frequency analysis of the complex signal, using the outputs from the first detection means and the second detection means as I signals and Q signals. The direction of speed can be determined by the sign of fd.

  The other is that the laser beam received by the receiving means is separated into a longer wavelength side and a shorter wavelength side than the wavelength of the laser beam and converted into an electrical signal, and the voltages of the two electrical signals are compared. Thus, a speed direction detecting means for detecting the speed direction of the object is provided.

  Alternatively, the distance may be measured a plurality of times, and the speed direction may be obtained from the time change of the distance.

  Since the receiving means may receive the laser beam reflected inside the radar apparatus and the distance measurement accuracy may be deteriorated, a means for correcting this may be provided.

  One of the correction means is to provide a recording means for recording the value of the internal reflection signal due to the reflection of the laser light inside the radar apparatus. The phase difference detection unit corrects the phase difference based on the value of the internal reflection signal of the recording unit and measures the distance to the object.

  Another one of the correction means is to receive the reflected light due to the reflection of the laser light inside the radar device, shift the phase of the reflected light by 180 °, and combine it with the laser light received by the receiving means. is there. As a result, the component due to internal reflection in the received laser light is canceled out, and only the component of laser light due to reflection from the object is corrected.

  For intensity modulation of laser light, an external modulation method may be used, or a direct modulation method may be used. The external modulation method is a method of intensity-modulating the output laser light by a modulator, and the direct modulation method is a method of directly outputting the intensity-modulated laser light by modulating the drive voltage.

  When the radar apparatus is used as an on-vehicle radar and an object having a speed of 0.5 to 50 m / s is to be measured, f0 is preferably 50 to 300 kHz, and the laser wavelength is preferably 0.8 to 1.7 μm. Within such a range, the distance speed of the object can be measured with high sensitivity and high accuracy.

  Another aspect of the present invention is a distance speed that measures the distance to the object and the speed of the object by irradiating the object with laser light and detecting and analyzing the laser light reflected by the object. In the measurement method, the object is irradiated with laser light that is intensity-modulated with a periodic signal having a frequency f0 smaller than the Doppler frequency fd due to the movement of the object, the laser light reflected by the object is received, and the received laser light And the laser beam before transmission are combined, optical heterodyne detection is performed to convert the signal into an electric signal, the phase difference between the frequency signal component of the electric signal f0 and the periodic signal is detected, and the distance to the object is measured. A distance speed measurement method characterized in that an electrical signal is subjected to frequency analysis to obtain a Doppler frequency fd and a speed is measured.

  In the radar apparatus of the present invention, the frequency f0 smaller than the Doppler frequency fd is set as the frequency of the periodic signal for intensity-modulating the laser light. Therefore, distance and speed can be measured separately. In addition, a relatively low-speed AD converter can be used when the electrical signal is digitally processed. Therefore, according to the radar apparatus of the present invention, it is possible to measure the distance and speed of an object with low cost and high accuracy.

1 is a diagram illustrating a configuration of a radar apparatus according to Embodiment 1. FIG. The figure which showed the waveform of a laser beam and an electrical signal. The figure which showed the structure of the speed direction detection means 22. FIG. FIG. 5 is a diagram illustrating a configuration of a radar apparatus according to a second embodiment. The figure which showed the structure of the radar apparatus of a modification. The figure which showed the example comprised by the optical integrated circuit. The figure explaining the measurement error by internal reflected light. The figure which showed the structure of the radar apparatus of a modification. The figure which showed the structure of the optical integrated circuit.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram illustrating a configuration of a radar apparatus according to the first embodiment. In FIG. 1, double-line arrows indicate laser beam paths, and single-line arrows indicate electrical signal paths. As shown in FIG. 1, the radar apparatus according to the first embodiment includes a laser 10, an oscillator 11, a modulator 12, a transmission unit 13, a reception unit 14, an optical BPF (bandpass filter) 15, a multiplexer 16, and a photodetector. 17, LPF (low-pass filter) 18, BPF (band-pass filter) 19, phase difference detection means 20, frequency analysis means 21, and speed direction detection means 22. BPF 18 and BPF 19 correspond to the first and second filters of the present invention, respectively. Hereinafter, each component will be described in detail.

  The laser 10 emits laser light that is continuous light having a wavelength of 1550 nm. Laser light output from the laser 10 is divided into two, one input to the modulator 12 and the other input to the multiplexer 16.

  The wavelength of the laser beam is not limited to 1550 nm, but it is desirable that the wavelength be in the range of 800 to 1700 nm in consideration of measurement accuracy, ease of generation, influence on the human body, and the like.

  The oscillator 11 generates a periodic signal that is a cosine wave having a frequency of 100 kHz. This periodic signal is input to the modulator 12 and the phase difference detection means 20.

  The periodic signal output from the oscillator 11 does not need to be a cosine wave as in the first embodiment, and may be an arbitrary signal as long as it is a periodic signal. For example, signals such as a triangular wave, a rectangular wave, and a sawtooth wave can be used. However, it is preferable to use a cosine wave in order to increase measurement sensitivity and improve measurement accuracy.

  The frequency of the periodic signal is determined by the speed of the object scheduled to be measured by the radar device. Specifically, the frequency of the periodic signal is set to a value sufficiently lower than the Doppler frequency fd generated by the motion of the object. The sufficiently low value is such that the frequency of the periodic signal and the Doppler frequency fd can be separated by a filter. By setting the frequency of the periodic signal in this way, it is possible to easily measure the distance and the speed simultaneously.

  For example, when the radar apparatus is mounted on a vehicle and used as an on-vehicle radar, the target is a pedestrian or a vehicle ahead. Since the relative speed with respect to these vehicles (that is, the relative speed v with respect to the radar device) is approximately 0.5 m / s to 50 m / s, the Doppler frequency fd is fd = 2 v / λ, where λ is the wavelength of the laser beam, From 0.65 to 65 MHz. Therefore, the frequency of the periodic signal may be a value sufficiently lower than 650 kHz, for example, 500 kHz or less. That is, any minimum value that can be measured for the Doppler frequency fd may be used. However, if the frequency is lower than 50 kHz, the measurement accuracy is deteriorated because it is smaller than the line width of the laser, which is not desirable. Therefore, in the first embodiment, the frequency is set to 100 kHz.

  Laser light from the laser 10 and a periodic signal from the oscillator 11 are input to the modulator 12. The modulator 12 modulates the intensity of the laser beam with a periodic signal and outputs it.

  The transmission means 13 is an optical system that irradiates the object with the laser light from the modulator 11 and is configured by an optical waveguide, a lens, or the like that guides the laser light in a predetermined direction.

  The receiving unit 14 is an optical system that collects and receives the laser light reflected by the object, and includes an optical waveguide, a condensing lens, a circuit that corrects the polarization state of the received laser light, and the like. The received laser beam is input to the light BPF 15.

  The transmission unit 13 and the reception unit 14 may be transmission / reception units that share transmission and reception by using an optical circulator or the like.

  Laser light from the receiving unit 14 is input to the optical BPF 15. The optical BPF 15 is an optical filter that transmits the wavelength band of the laser light and does not transmit the other bands. The output of the optical BPF 15 is input to the multiplexer 16. The light BPF 15 cuts out disturbance light and the like to improve the CN ratio, thereby improving the measurement accuracy of distance and speed.

  A laser beam from the light BPF 15 and a laser beam from the laser 10 are input to the multiplexer 16. The multiplexer 16 multiplexes these two laser beams and outputs them to the photodetector 17.

  Laser light from the multiplexer 16 is input to the photodetector 17. The photodetector 17 performs optical heterodyne detection on the input laser light, converts it into an electrical signal, and outputs it. The photodetector 17 is a photodiode. The output from the photodetector 17 is divided into two and input to the BPF 18 and the BPF 19 respectively.

  The BPF 18 is a filter that passes an input electric signal in the vicinity of the frequency of the periodic signal, that is, a frequency band in the vicinity of 100 kHz (for example, 90 to 110 kHz) and blocks and outputs the other bands. The electric signal output from the BPF 18 is input to the phase difference detection means 20.

  Note that the pass band of the BPF 18 is desirably in a range including a higher frequency than the fundamental frequency when a waveform including harmonics such as a rectangular wave and a triangular wave is used as the periodic signal from the oscillator 11. In addition, a low pass filter (LPF) may be used instead of the BPF 18 as long as it is a pass band including the fundamental frequency. For example, when a rectangular wave having a fundamental frequency of 100 kHz is used, an LPF that passes a frequency of 500 kHz or less and blocks other bands can be used.

  The BPF 19 is a filter that allows an input electric signal to pass through a frequency band of 500 kHz to 33 Mz and blocks and outputs the other bands. The electric signal output from the BPF 19 is input to the frequency analysis means 21.

  If the pass band includes a Doppler frequency, a high pass filter (HPF) may be used instead of the BPF 19. However, if the pass band is further limited using the BPF 19, the speed is obtained with higher accuracy. This is desirable.

  The BPFs 18 and 19 are not necessarily required for calculating the distance and speed by the radar apparatus of the first embodiment, but the signal processing in the phase difference detection means 20 and the frequency analysis means 21 is facilitated, and the distance and speed are increased. It is desirable to provide it for accurate measurement.

  The phase difference detection means 20 receives an electrical signal from the BPF 18 and a periodic signal from the oscillator 11. The phase difference detection means 20 detects the phase difference between the two signals input by the synchronous detection by the lock-in amplifier, and measures the distance of the object.

  The frequency analysis means 21 AD-converts the input electrical signal and performs FFT (Fast Fourier Transform). Then, the Doppler frequency is detected from the obtained frequency spectrum, and the speed of the object is measured. The direction of speed is separately measured by the speed direction detection means 22.

  An AD converter may be provided between the photodetector 17 and the BPF 18, and the signal processing after the BPF 18 may be digital processing. The BPF 18 may be analog processing and an AD converter may be provided in the phase difference detection means 20 to provide a phase difference. The signal processing in the detection means 20 may be digital processing. Similarly, the signal processing after BPF 19 may be digital processing, or BPF 19 may perform analog processing and frequency analysis means 21 may be digital processing. The BPFs 18 and 19, the phase difference detection unit 20, and the frequency analysis unit 21 may be configured by a DSP (digital signal processor).

  The laser beam from the light BPF 15 is input to the speed direction detection unit 22. The speed direction detecting means 22 measures the direction of the speed of the object, that is, whether the object is approaching or moving away from the radar apparatus, from the input laser beam.

  Note that the speed direction detecting means 22 is not necessary when it is not necessary to detect the speed direction. Alternatively, the speed direction detecting means 22 may not be provided, the distance may be measured a plurality of times, and the speed direction may be determined from the increase or decrease in the distance.

  Next, the operation for measuring the distance and speed of the object by the radar apparatus according to the first embodiment will be described in detail.

  Laser light output from the laser 10 is distributed and one is input to the modulator 12 and the other is input to the multiplexer 16. The laser beam input to the modulator 12 is intensity-modulated with a periodic signal from the oscillator 11 that is a cosine wave having a single frequency and output. FIG. 2A shows the waveform of the periodic signal, and FIG. 2B shows the waveform of the intensity-modulated laser beam. Here, if the angular frequency of the laser light is ω and the angular frequency of the periodic signal is ω0, the intensity-modulated laser light includes three angular frequency components of angular frequencies ω, ω + ω0, and ω−ω0.

  The intensity-modulated laser light is applied to an object outside the radar apparatus by the transmission means 13. Then, the laser beam reflected by the object is received by the receiving means 14. Here, when the object is moving at a relative speed v with respect to the radar device, the frequency of the received laser light is shifted by the Doppler effect. If the Doppler frequency is fd and ωd = 2π · fd, then v = c · ωd / (2ω). Here, c is the speed of light. Therefore, each angular frequency component of the received laser light is three components of ω + ωd, ω + ωd + ω0, and ω + ωd−ω0. Note that the sign of ωd is positive in the direction in which the object approaches the radar apparatus and negative in the direction in which the object moves away.

  Laser light received by the receiving means 14 is distributed after disturbance light or the like is cut by the light BPF 15, and one is combined with the laser light from the laser 10 in the multiplexer 16 and input to the photodetector 17. The The other is input to the speed direction detection means 22.

  The laser light input to the photodetector 17 is subjected to optical heterodyne detection, and the difference frequency component is output as an electrical signal. The angular frequency includes five components ωd, ωd + ω0, ωd−ω0, ω0, and 2ω0. Thus, by using optical heterodyne detection, the distance and speed can be measured with high sensitivity. As a reference, FIG. 2C shows a waveform of an electric signal having two components ωd and ω0 required in the following signal processing.

  The electric signal output from the photodetector 17 is divided into two and input to the BPFs 18 and 19, respectively.

  The electrical signal input to the BPF 18 passes only in the band near the angular frequency ω0, and other angular frequency components are blocked. Then, the electrical signal that has passed through the BPF 18 is input to the phase difference detection means 20.

  The phase difference detection means 20 receives the periodic signal from the oscillator 11 and the electrical signal from the BPF 18. FIG. 2D shows the waveform of the electric signal. Then, a DC voltage value of cos Δφ and sin Δφ (where Δφ is the phase difference between the periodic signal and the electric signal from the BPF 18) is obtained by synchronous detection by the lock-in amplifier, and the phase difference Δφ is calculated from the value. The distance R from the radar device to the object can be calculated by R = c · Δφ / (2ω0). Since the lock-in amplifier is used, the phase difference Δφ can be measured with high accuracy and high resolution, and therefore the distance R can also be measured with high accuracy and high resolution. As a result, the phase difference Δφ can be obtained with high accuracy even if a relatively low-speed device is used as the AD converter when the electrical signal is digitally processed.

  On the other hand, the electrical signal input to the BPF 19 passes only through the band near the angular frequency ωd, and other angular frequency components are blocked. The electrical signal that has passed through the BPF 19 is input to the frequency analysis means 21. FIG. 2E shows the waveform of the electrical signal that has passed through the BPF 19.

  The frequency analysis means 21 calculates the velocity v of the object by performing frequency analysis on the input electrical signal as follows. First, a frequency spectrum of an electric signal input by FFT (Fast Fourier Transform) is calculated. Then, the Doppler frequency fd (= ωd / 2π) is obtained from the peak position of the frequency spectrum. When the Doppler frequency fd is obtained, v = λ · fd / 2, where λ is the wavelength of the laser beam output from the laser 10, and the velocity v of the object can be calculated.

  As described above, in the radar apparatus according to the first embodiment, by setting the frequency of the periodic signal to a value lower than the Doppler frequency, it is possible to separate the received electrical signal into the frequency of the periodic signal and the signal of the Doppler frequency. Thus, the distance and speed can be measured by the phase difference detection means 20 and the frequency analysis means 21, respectively.

  The frequency analysis means 21 can measure the speed, but cannot measure the direction of speed (whether the object is approaching or moving away from the radar apparatus). Therefore, the direction is measured by the speed direction detection means 22 as follows.

  The velocity direction detection means 22 measures the velocity direction by measuring whether the wavelength of the received laser beam is shifted to the longer wavelength side or the shorter wavelength side with respect to the oscillation wavelength of the laser 10.

  FIG. 3 is a diagram showing a specific configuration of the speed direction detection means 22. As shown in FIG. 3, the speed direction detection unit 22 includes a ring resonator type filter 100, two photodiodes 101 and 102, and a comparator 103. A part of the laser light transmitted through the light BPF 15 is input to the ring resonator type filter 23 of the velocity direction detection means 22. The ring resonator type filter 23 separates the inputted laser light into a long wavelength side and a short wavelength side around the output wavelength λ of the laser 10. Then, the laser light on the long wavelength side and the laser light on the short wavelength side are converted into electric signals by the photodiodes 101 and 102, respectively. The electrical signals output from the photodiodes 101 and 102 are input to the comparator 03. In the comparator 103, an output corresponding to the voltage difference between the two input electric signals is obtained.

  Here, when the object is moving in the direction approaching the radar apparatus, the wavelength of the laser light is shifted to the short wavelength side due to the Doppler effect, and when the object is moving in the direction away from the radar apparatus, the wavelength is shifted to the long wavelength side. Therefore, the electrical signals output from the photodiodes 101 and 102 have a difference in voltage according to the wavelength shift. When the wavelength is shifted to the long wavelength side, the voltage of the electric signal from the photodiode 101 is larger, and when the wavelength is shifted to the short wavelength side, the electric signal from the photodiode 102 is larger. Increases the voltage. Therefore, by detecting which voltage is larger by the comparator 103, it can be determined whether the wavelength is shifted to the long wavelength side or the short wavelength side, and the direction of the speed of the object can be determined.

  As described above, according to the radar apparatus of the first embodiment, the distance and speed of the target can be measured with high sensitivity and high accuracy. In addition, since a relatively low-speed device can be used as an AD converter in the case of digital processing, and the laser light processing portion in the radar apparatus can be modularized by an optical integrated circuit, the radar apparatus according to the first embodiment is It is easy to reduce the cost.

  FIG. 4 is a diagram illustrating a configuration of the radar apparatus according to the second embodiment. The radar apparatus according to the second embodiment is the same as the radar apparatus according to the first embodiment except that a π / 2 phase shifter 200, a multiplexer 201, a photodetector 202, and a BPF 203 are added, and the frequency analyzing means 210 is replaced with the frequency analyzing means 21. The speed direction detecting means 22 is omitted. Other configurations are the same as those of the first embodiment. As the multiplexer 201, the photodetector 202, and the BPF 203, those having the same performance as the multiplexer 16, the photodetector 17, and the BPF 19 of the first embodiment are used. Hereinafter, the components different from the first embodiment will be described, and the operation of the radar apparatus of the second embodiment will be described.

  Laser light output from the laser 10 is distributed and input to the modulator 12, the multiplexer 16, and the π / 2 phase shifter 200. Laser light from the laser 10 is input to the π / 2 phase shifter 200, and π / 2 phase is shifted and output to the multiplexer 201.

  The laser light output from the optical BPF 15 is distributed and input to the multiplexers 16 and 201. The multiplexer 201 receives the laser light from the π / 2 phase shifter 200 and the laser light from the optical BPF 15, multiplexes them, and outputs them.

  The photodetector 202 detects the input laser beam by optical heterodyne, converts it into an electrical signal, and outputs it to the frequency analysis means 210 via the BPF 203. Similarly to the first embodiment, the photodetector 17 optically heterodyne-detects the laser beam input from the multiplexer 16 and converts it into an electrical signal, which is output to the frequency analysis means 210 via the BPF 19. That is, the electrical signal output from the photodetector 17 is an I signal, and the electrical signal output from the photodetector 202 is a Q signal.

  The frequency analysis means 210 receives electrical signals (I signal and Q signal) from the BPF 19 and the BPF 203. The frequency analysis unit 210 uses a complex signal having a real part as an I signal and an imaginary part as a Q signal, calculates the frequency spectrum by performing FFT on the complex signal, and calculates the Doppler frequency including positive and negative from the peak of the frequency spectrum. To do. Then, the speed is calculated from the absolute value of the Doppler frequency, and the direction of the speed is calculated from the sign of the Doppler frequency. A positive Doppler frequency is obtained when the object is approaching the radar apparatus, and a negative Doppler frequency is obtained when the object is moving away.

  Note that the distance to the object is measured in the same manner as the radar apparatus of the first embodiment. That is, the distance is calculated from the phase difference between the electrical signal from the BPF 18 and the periodic signal from the oscillator 11.

  As described above, in the radar apparatus according to the second embodiment, an optical heterodyne detection is performed by the multiplexer 16 and the photodetector 17 to generate an I signal, and the π / 2 phase shifter 200, the multiplexer 201, and the photodetector 202 are generated. Thus, the optical heterodyne detection is performed by shifting the phase by 90 ° with the laser light as it is to generate the Q signal. That is, the configuration is such that orthogonal detection and optical heterodyne detection are performed simultaneously. Then, a complex signal is composed of the I signal and Q signal obtained thereby, and FFT is performed to calculate the Doppler frequency including positive and negative to obtain the speed and its direction.

  According to the radar apparatus of the second embodiment, as with the radar apparatus of the first embodiment, the distance and speed of the target can be measured with high sensitivity and high accuracy.

  In the second embodiment, when optical heterodyne detection is performed by the photodetector 202, the laser beam received by the receiving unit 14 is phase-shifted by the π / 2 phase shifter 200 instead of the laser beam output from the laser 10. The Q signal may be generated in the photodetector 202 by shifting the angle by 90 °.

[Variations]
The means for detecting the speed direction is not limited to the first and second embodiments, and various conventionally known methods can be used. For example, the distance may be measured a plurality of times, and the speed direction may be obtained from the time change of the distance.

  The radar apparatus according to the first and second embodiments is an external modulation method in which laser light from a laser is externally modulated by the modulator 12, but the present invention is also applied to a direct modulation method in which intensity modulation is directly performed by controlling the laser drive current. The invention can be applied.

  As an example, FIG. 5 shows a configuration when the external modulation system is changed to the direct modulation system in the second embodiment. As shown in FIG. 5, the modulator 12 is omitted, and a laser 300 is provided instead of the laser 10. A periodic signal from the oscillator 11 is input to the laser 300. The laser 300 modulates the drive current based on the periodic signal from the oscillator 11 and outputs laser light whose intensity is modulated by the periodic signal. The modulated laser light is distributed and input to the transmission means 13, the multiplexer 16, and the π / 2 phase shifter 200. Since the modulated laser beams are input to the multiplexers 16 and 201, the frequency components other than those in the second embodiment, ωd + 2ω0 and ωd−2ω0 are also included in the electrical signals output from the photodetectors 17 and 202. included. If correction is made in consideration of these frequency components, the Doppler frequency ωd can be calculated in the same manner as in the second embodiment to measure the speed of the object. Of the electrical signals output from the photodetectors 17 and 202, the component having a frequency of ω0 includes a component in which no phase difference from the periodic signal from the oscillator 11 occurs. Therefore, if the correction is performed accordingly, the distance can be measured by detecting the phase difference in the phase difference detecting means 20 as in the second embodiment.

  In the radar apparatus according to the first and second embodiments, the component that processes the laser beam may be configured by an optical integrated circuit. As an example, FIG. 6 shows a configuration in which the laser beam processing portion in the radar apparatus of the second embodiment is an optical integrated circuit. The correspondence between each element of the optical integrated circuit and the components of the second embodiment will be described.

A structure in which Si is formed in a line shape on a SiO ₂ substrate is used for the optical waveguide 300 that connects each component. A coupler 301 is used to distribute the optical waveguide 300. Further, a ring modulator 302 is used as the modulator 12. Further, the transmitting means 13 is configured to radiate to the outside as it is from the end face of the optical waveguide 300. As the receiving means 14, a polarization correction diffraction grating 303 is used. By correcting the polarization state of the laser beam received by the polarization correction diffraction grating 303, the coupling with the optical waveguide 300 is improved. A ring resonator 304 is used as the optical BPF 15. As the π / 2 phase shifter 200, a heater is disposed on the optical waveguide and the position is modulated by the thermo-optic effect by the heat of the heater. A photodiode 305 is used for the photodetectors 17 and 202. Further, a VOA (variable optical attenuator) 306 is inserted into the optical waveguide 300 so that the intensity of the laser light input from the laser 10 to the photodiode 305 can be adjusted.

  As described above, by modularizing the laser light processing portion of the radar apparatus according to the first and second embodiments as an optical integrated circuit, the cost of the radar apparatus can be reduced.

  Further, in the radar devices of the first and second embodiments, the reflected light of the laser beam inside the radar device is received, and the measurement accuracy may be deteriorated. As shown in FIG. 7, when the internal reflection signal is added to the real signal, the vector of the measurement signal actually measured is a vector obtained by adding the vector of the real signal and the vector of the internal reflection signal. Therefore, the measurement signal is different in phase from the actual signal. As a result, an error occurs in the distance measurement. Therefore, it is conceivable to correct the internal reflection signal so that the actual signal can be extracted by adding together signals having opposite vectors and the same magnitude. This is possible, for example, by the following two methods.

  One is a method of recording the value of the internal reflection signal and subtracting it from the measurement signal to obtain a real signal. The internal reflection signal is caused by the structure of the laser device or the installation environment of the laser device, and always takes a constant value. Therefore, the value of the internal reflection signal is recorded in the recording means at the time of shipment from the factory and the value is subtracted by the phase difference detecting means 20 to correct it to an actual signal. FIG. 8 shows an example in which such a recording unit 400 is provided in the radar apparatus of the second embodiment. For example, the correction is performed by subtracting the correction data α and β held by the recording unit 400 from cos Δφ and sin Δφ which are outputs from the lock-in amplifier in the phase difference detection unit 20 to obtain cos Δφ-α and sin Δφ-β.

  The other is a method of separately receiving reflected light due to internal reflection, shifting the phase by 180 °, and then combining the received laser light. Since correction is performed at the stage of laser light, it is highly sensitive. FIG. 9 is obtained by adding such correction means to the optical integrated circuit of FIG. As shown in FIG. 9, it further includes a lens 500, a polarization correction diffraction grating 501, a filter 502, a VOA 503, and a coupler 504. The lens 500 collects laser light (reflected light) reflected inside the radar apparatus and makes it incident on the polarization correction diffraction grating 501. The reflected light whose polarization state is corrected by the polarization correction diffraction grating 501 passes through the filter 502, and then the light intensity is adjusted by the VOA 503 and the phase is shifted by 180 °. Then, the laser beam that has passed through the filter 304 is multiplexed by the coupler 504. As a result, the reflected light component of the received laser light is canceled, and correction can be made only to the reflected light component from the object.

  Moreover, when using the radar apparatus of this invention as a vehicle-mounted radar, a target object is a pedestrian, a front vehicle, etc., and the speed is about 0.5-50 m / s. At this time, the frequency f0 of the periodic signal from the oscillator 11 is 50 to 300 kHz, and the wavelength of the laser is 800 to 1700 nm, so that the distance and speed of the object can be measured systematically.

  The radar apparatus of the present invention can be used for in-vehicle radar and the like, and can detect pedestrians and the like.

10: Laser 11: Oscillator 12: Modulator 13: Transmitting means 14: Receiving means 15: Optical BPF
16, 201: multiplexer 17, 202: photodetector 18, 19, 203: BPF
20: Phase detection means 21, 210: Frequency analysis means 22: Speed direction detection means 200: π / 2 phase shifter 400: Recording means

Claims (13)

In a radar apparatus that measures the distance to the object and the speed of the object by irradiating the object with laser light and detecting and analyzing the laser light reflected by the object,
Transmitting means for irradiating the object with laser light intensity-modulated with a periodic signal having a frequency f0 smaller than the minimum measurable Doppler frequency fd by the movement of the object;
Receiving means for receiving the laser light reflected by the object;
Detecting means for combining the laser light received by the receiving means and the laser light before transmission to detect optical heterodyne and convert it into an electrical signal;
A phase difference detection means for detecting a phase difference between the frequency signal component of the electrical signal from the detection means and the periodic signal and measuring a distance to the object;
Frequency analysis means for obtaining a Doppler frequency fd by frequency-analyzing the electrical signal from the detection means and measuring speed;
A radar apparatus comprising: A first filter between the detection means and the phase difference detection means;
The first filter sets a predetermined frequency that is equal to or higher than the frequency f0 and equal to or lower than the Doppler frequency fd as f1, transmits a frequency band equal to or lower than f1, and blocks and outputs the other bands.
The radar apparatus according to claim 1. Having a second filter between the detection means and the frequency analysis means;
The second filter has a predetermined frequency that is equal to or higher than the frequency f0 and equal to or lower than the Doppler frequency fd as f1, a predetermined frequency that is equal to or higher than f1 and equal to or lower than the Doppler frequency fd as f2, and transmits the frequency band equal to or higher than f2 to other bands. Shut off and output,
The radar apparatus according to claim 1 or 2, wherein   The radar apparatus according to any one of claims 1 to 3, wherein the periodic signal is a cosine wave.   The radar apparatus according to any one of claims 1 to 4, wherein the transmission unit, the reception unit, and the detection unit are configured by an optical integrated circuit. The detecting means combines first laser light received by the receiving means and laser light before transmission to detect optical heterodyne, and the laser light received by the receiving means and laser before transmission. A second detection means for shifting one phase of the light by 90 ° to multiplex, and optical heterodyne detection;
The frequency analyzing means analyzes the frequency of the complex signal by using the outputs from the first detecting means and the second detecting means as I signals and Q signals, and obtains the speed from the Doppler frequency fd. The direction of speed is detected by the sign of frequency fd.
The radar apparatus according to any one of claims 1 to 5, wherein the radar apparatus is characterized in that: The laser light received by the receiving means is separated into a longer wavelength side and a shorter wavelength side than the wavelength of the laser light, respectively converted into an electric signal, and the voltage of two electric signals is compared, thereby the object A speed direction detecting means for detecting a speed direction of the object;
The radar apparatus according to any one of claims 1 to 5, wherein the radar apparatus is characterized in that: It further comprises recording means for recording the value of the internal reflection signal due to the reflection of the laser light inside the radar device,
The phase difference detection means corrects the phase difference based on the value of the internal reflection signal of the recording means and measures the distance to the object.
The radar apparatus according to claim 1, wherein the radar apparatus is characterized. A correction unit that corrects the laser beam received by the receiving unit by receiving the reflected light due to the reflection of the laser beam inside the radar apparatus and shifting the phase of the reflected light by 180 ° and combining the received light;
The radar apparatus according to claim 1, wherein the radar apparatus is characterized.   The radar apparatus according to any one of claims 1 to 9, wherein the radar apparatus is an external modulation system in which laser light is intensity-modulated by a modulator.   10. The radar apparatus according to claim 1, wherein the radar apparatus is a direct modulation system that generates laser light that is intensity-modulated by modulation of a drive voltage.   The radar device is an on-vehicle radar, and an object having a speed of 0.5 to 50 m / s is measured, f0 is 50 to 300 kHz, and a laser wavelength is 0.8 to 1.7 μm. The radar device according to any one of claims 1 to 11. In the distance-velocity measuring method for measuring the distance to the object and the speed of the object by irradiating the object with laser light and detecting and analyzing the laser light reflected by the object,
Irradiating the object with laser light intensity-modulated with a periodic signal having a frequency f0 smaller than a minimum value of the Doppler frequency fd that can be measured by the movement of the object;
Receiving the laser light reflected by the object;
The received laser beam and the laser beam before transmission are combined, optical heterodyne detection is performed and converted into an electrical signal,
Detecting the phase difference between the frequency signal component of the electrical signal f0 and the periodic signal to measure the distance to the object;
Frequency analysis of the electrical signal to obtain a Doppler frequency fd and to measure the speed;
A distance speed measurement method characterized by the above.

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